1. Field of the Invention
The present invention relates to a video cassette recorder, and more particularly to a reel table driving mechanism for a video cassette recorder which can transmit drive forces of different torques to a supply reel table and a take-up reel table in accordance with operating modes thereof.
2. Prior Art
Generally, a video cassette recorder (hereinafter, simply referred to VCR) is a device for recording/reproducing an image signal and an audio signal onto/from a magnetic tape running along a running system. The magnetic tape is wound around a pair of reels provided in a cassette. When the cassette is loaded into a deck of the VCR according to a loading mechanism, the pair of reels are respectively mounted on a take-up reel table and a supply reel table installed on the deck. After that, the take-up reel table and the supply reel table are rotated by a capstan motor, thereby carrying out selected operating modes such as play, record, fast forward and rewind. At this time, the magnetic tape is drawn out from one reel and is wound around the other reel according to the rotating directions of the take-up reel table and the supply reel table.
A typical reel disc driving system of a conventional VCR 500 is schematically shown in FIG. 5, wherein a tape 501 may be made to travel in a forward or a reverse direction by the drive of a supply reel table 510 or a take-up reel table 520. Further, tape 501 can be made to travel at a constant speed by means of a capstan shaft 550 and a pinch roller 540. In general, reel tables 510 and 520 are selectively driven by an idler 560 for transmitting the driving force of a capstan motor 530.
Idler 560 is selectively engaged with supply reel table 510 or take-up reel table 520 according to a rotating direction of capstan motor 530 so that supply reel table 510 or take-up reel table 520 can be selectively rotated. However, looseness of loaded magnetic tape 501 may occur during the conversion from one mode to another mode of operation due to a delay in the shifting motion of idler 560 and an inertia moment of reel tables 510 and 520, which may cause operational failures, noises and/or distortions.
Therefore, take-up reel table 520 requires relatively less torque for running magnetic tape 501 in the forward direction because it is disposed closer to capstan motor 530, whereas supply reel table 510 requires relatively more torque for moving magnetic tape 501 in the reverse direction because it is disposed farther from capstan motor 530.
Moreover, in case of the rewind or fast forward modes wherein magnetic tape 501 is run at a higher speed, a higher level of torque is required for rotating reel tables 510 and 520. Such requirements for varying the torque of each reel table are normally executed by means of a reel disc driving mechanism.
FIG. 6 shows a conventional reel table driving mechanism 300 for VCR 500. As shown in FIG. 6, reel table driving mechanism 300 comprises a first rotator 12 rotatably mounted to a support shaft 14 which is secured to a deck. a driving pulley 18 rotatably inserted around a hub 13 of first rotator 12 and in contact with first rotator 12 through a felt member 34, and a second rotator 22 firmly fitted on hub 13 of first rotator 12. A movable member 20 is coupled to second rotator 22 so that it is selectively engaged with openings 32 of driving pulley 18 so as to directly transmit the drive force of pulley 18 to second rotator 22.
In addition, seated at second rotator 22 is a spring 24 which can bias movable member 20 upward to separate it from openings 32 of driving pulley 18, thereby transmitting the driving force of pulley 18 to first rotator 12 through felt member 34.
A driving gear 10 is rotatably inserted around hub of first rotator 12 and meshed with idler 560. Also, disposed between second rotator 22 and driving gear 10 is a spring 26 which pushes driving gear 10 upward to properly engage it with idler. Pulley 18 is rotated clockwise or counterclockwise through a belt 30 coupled thereto, depending on a forward or a reverse driving of capstan motor 530.
In the case of a play or a review mode, movable member 20 is kept separated from pulley 18. Therefore, the driving force of pulley 18 is transmitted to first rotator 12 due to the frictional contact therebetween via felt member 34, providing driving gear 10 with relatively less torque through second rotator 22 and spring 26. As a result, idler 560 is shifted toward and engaged with one of reel tables 510 and 520, thereby operating VCR 500 in a desired mode. When an excess load is exerted against driving gear 10 during an operation of VCR 500, a slippage between pulley 18 and first rotator 12 occurs, preventing loaded tape 501 from slackening.
In the case of a rewind mode or a fast forward mode, movable member 20 is pressed downward against the biasing force of spring 24 by a pressing member (not shown) and then engaged with driving pulley 18 through openings 32 of pulley 18. Therefore, pulley 18 and second rotator 22 are rotated together with first rotator 12. Accordingly, the driving force of pulley 18 is directly transmitted to gear 10 to generate a higher torque for each reel table, enabling VCR 500 to operate in the rewind or fast forward operating mode.
However, while the play mode or the review mode is being carried out, conventional reel table driving mechanism 300 transmits the same torque to supply reel table 510 or take-up reel table 520 so that the looseness or slackening of the loaded magnetic tape may occur while the above modes are executed.